The present invention relates to an electrophotographic printing apparatus equipped with a liquid development unit for developing a latent electrostatic image, formed on a surface of a photoconductive member, with liquid developer.
A conventional electrophotographic printing apparatus is disclosed in U.S. Pat. No. 4,268,597, which issued to Klavan et al. on May 19, 1981. The printing apparatus includes a liquid development unit which has a container for storing liquid developer and a developer roller rotatably provided and partially submerged in the liquid developer. The developer roller is located opposite a photoconductive member such that there is a small gap between opposing surfaces of the developer roller and photoconductive member.
In a developing operation, as the developer roller rotates, a film of the liquid developer is formed on the surface of the developer roller at a position close to the photoconductive member. The liquid developer film is partially attracted and then adheres to an electrostatic image which has been formed on the surface of the photoconductive member by electrostatic force.
In such a development unit, it is important to make the gap between the developer roller and photoconductive member small and constant in order to develop a fine electrostatic image. To this end, it is effective to provide a pair of spacer members between the developer roller and photoconductive member; the Klavan et al. patent discloses, in FIGS. 29 and 30, spacer annuli provided on both ends of the photoconductive member.
The conventional printing apparatus has, however, a disadvantage in that the liquid developer stagnates between the developer roller and the photoconductive member initially at the portions where the spacer members are provided due to the surface tension of the liquid developer. As a result, the gap tends to be stopped up with the liquid developer, causing the surface of the photoconductive member to be improperly developed. More specifically, the liquid developer adheres to the area of the photoconductive member's surface where the electrostatic image is not formed.